1. Field of the Invention
The present invention relates to a method for measuring a location of a mobile terminal and, more particularly, to a method for measuring a location of a mobile terminal according to a ToA (Time of Arrival) scheme or according to a combination of the ToA scheme and an AoA (Angle of Arrival) scheme by using a plurality of base station signals and collecting location information by using angle information between the mobile terminal and base stations, thus reducing a location measurement error when the base stations and the mobile terminal are located within a short distance.
2. Description of the Related Art
Recently, research into a technique for measuring a location of a mobile terminal in a communication network is actively ongoing in line with the development of a mobile communication technology.
Methods for measuring a location of a mobile terminal include a technique of recognizing an accurate location of a service requesting terminal by using a Global Positioning System (GPS) or utilizing the location of a base station of a wireless network, a network scheme and a terminal scheme, a hybrid scheme combining these methods, and the like.
The GPS using signals received from artificial satellites is dependent upon the strength of the satellite signals, a GPS receiver needs be installed in a location measurement target terminal, and the GPS cannot be used in an indoor area in which a GPS reception is not available. Thus, in order to solve this limitation, methods for estimating the location of a mobile terminal by using the mobile communication characteristics such as GSM, CDMA, and the like, have been frequently introduced. Typical examples of the methods include a Cell ID for recognizing the location of a user through a service cell ID of a base station to which the user belongs, AoA (Angle Of Arrival) using the difference in a signal reception angle in three base stations which have received a signal of a terminal, ToA (Time Of Arrival) using the difference in a signal arrival time between one base station and two neighbor base stations, TDoA for measuring a signal delay of adjacent base stations based on a base station signal, and the like.
The location measurement methods are on the assumption that three or more base station signals can be received; however, the probability in which a terminal receives three or more base station signals is 92% in downtown and merely 71% in rural areas, indicating that the accuracy of the location measurement is low.
Also, the location measurement method is based on the assumption that a base station and a terminal are located to be sufficiently far away from each other. With reference to FIG. 1A, when the base station and the terminal are located to be sufficiently far away from each other, a vertical distance h1 from a plane on which the terminal is located to the base station is sufficiently small compared with the distance d1 from the base station to the terminal, having the relationship of d1≠d1′, so the location information according to ToA is calculated by using d1 to measure the location of the terminal. However, when the base station and the terminal are located within a short distance as shown in FIG. 1B, a vertical distance h2 from a plane on which the terminal is located to the base station is not sufficiently small compared with the distance d2 from the base station to the terminal, having the relationship of d2≠d2′. Thus, in this case, if the location information according to ToA is calculated by using d2, a great error would be generated in measuring the location of the terminal.